Methods to partially reduce a niobium metal oxide and oxygen reduced niobium oxides

ABSTRACT

Methods to at least partially reduce a niobium oxide are described wherein the process includes heat treating the niobium oxide in the presence of a getter material and in an atmosphere which permits the transfer of oxygen atoms from the niobium oxide to the getter material, and for a sufficient time and at a sufficient temperature to form an oxygen reduced niobium oxide. Niobium oxides and/or suboxides are also described as well as capacitors containing anodes made from the niobium oxides and suboxides.

This application is a divisional of U.S. patent application Ser. No.09/533,430 filed Mar. 23, 2000, which is a continuation-in-part of U.S.patent application Ser. No. 09/347,990 filed Jul. 6, 1999, and U.S.patent application Ser. No. 09/154,452 filed Sep. 16, 1998, which areincorporated herein in their entirety by reference.

BACKGROUND OF THE INVENTION

The present invention relates to niobium and oxides thereof and moreparticularly relates to niobium oxides and methods to at least partiallyreduce niobium oxide and further relates to oxygen reduced niobium.

SUMMARY OF THE PRESENT INVENTION

In accordance with the purposes of the present invention, as embodiedand described herein, the present invention relates to a method to atleast partially reduce a niobium oxide which includes the steps of heattreating the niobium oxide in the presence of a getter material and inan atmosphere which permits the transfer of oxygen atoms from theniobium oxide to the getter material for a sufficient time andtemperature to form an oxygen reduced niobium oxide.

The present invention also relates to oxygen reduced niobium oxideswhich preferably have beneficial properties, especially when formed intoan electrolytic capacitor anode. For instance, a capacitor made from theoxygen reduced niobium oxide of the present invention can have acapacitance of up to about 200,000 CV/g or more. Further, electrolyticcapacitor anodes made from the oxygen reduced niobium oxides of thepresent invention can have a low DC leakage. For instance, such acapacitor can have a DC leakage of from about 0.5 nA/CV to about 5.0nA/CV.

Accordingly, the present invention also relates to methods to increasecapacitance and reduce DC leakage in capacitors made from niobiumoxides, which involves partially reducing a niobium oxide by heattreating the niobium oxide in the presence of a getter material and inan atmosphere which permits the transfer of oxygen atoms from theniobium oxide to the getter material, for a sufficient time andtemperature to form an oxygen reduced niobium oxide, which when formedinto a capacitor anode, has reduced DC leakage and/or increasedcapacitance.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory onlyand are intended to provide further explanation of the presentinvention, as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-11 are SEMs of various oxygen reduced niobium oxides of thepresent invention at various magnifications.

FIG. 12 is a graph plotting DC leakage vs. Formation voltage for aniobium oxide capacitor anode and other anodes made from niobium ortantalum.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

In an embodiment of the present invention, the present invention relatesto methods to at least partially reduce a niobium oxide. In general, themethod includes the steps of heat treating a starting niobium oxide inthe presence of a getter material in an atmosphere which permits thetransfer of oxygen atoms from the niobium oxide to the getter materialfor a sufficient time and at a sufficient temperature to form an oxygenreduced niobium oxide.

For purposes of the present invention, the niobium oxide can be at leastone oxide of niobium metal and/or alloys thereof. A specific example ofa starting niobium oxide is Nb₂O₅.

The niobium oxide used in the present invention can be in any shape orsize. Preferably, the niobium oxide is in the form of a powder or aplurality of particles. Examples of the type of powder that can be usedinclude, but are not limited to, flaked, angular, nodular, and mixturesor variations thereof. Preferably, the niobium oxide is in the form of apowder which more effectively leads to the oxygen reduced niobium oxide.

Examples of such preferred niobium oxide powders include those havingmesh sizes of from about 60/100 to about 100/325 mesh and from about60/100 to about 200/325 mesh. Another range of size is from −40 mesh toabout −325 mesh.

The getter material for purposes of the present invention is anymaterial capable of reducing the specific starting niobium oxide to theoxygen reduced niobium oxide. Preferably, the getter material comprisestantalum, niobium, or both. More preferably, the getter material istantalum. The tantalum getter material for purposes of the presentinvention is any material containing tantalum metal which can remove orreduce at least partially the oxygen in the niobium oxide. Thus, thetantalum getter material can be an alloy or a material containingmixtures of tantalum metal with other ingredients. Preferably, thetantalum getter material is predominantly, if not exclusively, tantalummetal. The purity of the tantalum metal is not important but it ispreferred that high purity tantalum metal comprise the getter materialto avoid the introduction of other impurities during the heat treatingprocess. Accordingly, the tantalum metal in the tantalum getter materialpreferably has a purity of at least about 98% and more preferably atleast about 99%. Further, it is preferred that impurities such as oxygenare not present or are present in amounts below about 100 ppm.

The getter material can be in any shape or size. For instance, thegetter material can be in the form of a tray which contains the niobiumoxide to be reduced or can be in a particle or powder size. Preferably,the getter materials are in the form of a powder in order to have themost efficient surface area for reducing the niobium oxide. The gettermaterial, thus, can be flaked, angular, nodular, and mixtures orvariations thereof. Preferably, the getter material is a tantalumhydride material. A preferred form is coarse chips, e.g. 14/40 meshchips that can be easily separated from the powder product by screening.

Similarly, the getter material can be niobium and the like and can havethe same preferred parameters and/or properties discussed above for thetantalum getter material. Other getter materials can be used alone or incombination with the tantalum or niobium getter materials. Also, othermaterials can form a part of the getter material.

Generally, a sufficient amount of getter material is present to at leastpartially reduce the niobium oxide being heat treated. Further, theamount of the getter material is dependent upon the amount of reducingdesired to the niobium oxide. For instance, if a slight reduction in theniobium oxide is desired, then the getter material will be present in astoichemetric amount. Similarly, if the niobium oxide is to be reducedsubstantially with respect to its oxygen presence, then the gettermaterial is present in a 2 to 5 times stoichemetric amount. Generally,the amount of getter material present (e.g. based on the tantalum gettermaterial being 100% tantalum) can be present based on the followingratio of getter material to the amount of niobium oxide present of fromabout 2 to 1 to about 10 to 1.

Furthermore, the amount of getter material can also be dependent on thetype of niobium oxide being reduced. For instance, when the niobiumoxide being reduced is Nb₂O₅, the amount of getter material ispreferably 5 to 1.

The heat treating that the starting niobium oxide is subjected to can beconducted in any heat treatment device or furnace commonly used in theheat treatment of metals, such as niobium and tantalum. The heattreatment of the niobium oxide in the presence of the getter material isat a sufficient temperature and for a sufficient time to form an oxygenreduced niobium oxide. The temperature and time of the heat treatmentcan be dependent on a variety of factors such as the amount of reductionof the niobium oxide, the amount of the getter material, and the type ofgetter material as well as the type of starting niobium oxide.Generally, the heat treatment of the niobium oxide will be at atemperature of from less than or about 800° C. to about 1900  C. andmore preferably from about 1000° C. to about 1400° C., and mostpreferably from about 1200° C. to about 1250° C. In more detail, whenthe niobium oxide is a niobium containing oxide, the heat treatmenttemperatures will be from about 1000° C. to about 1300° C., and morepreferably from about 1200° C. to about 1250° C. for a time of fromabout 5 minutes to about 100 minutes, and more preferably from about 30minutes to about 60 minutes. Routine testing in view of the presentapplication will permit one skilled in the art to readily control thetimes and temperatures of the heat treatment in order to obtain theproper or desired reduction of the niobium oxide.

The heat treatment occurs in an atmosphere which permits the transfer ofoxygen atoms from the niobium oxide to the getter material. The heattreatment preferably occurs in a hydrogen containing atmosphere where ispreferably just hydrogen. Other gases can also be present with thehydrogen, such as inert gases, so long as the other gases do not reactwith the hydrogen. Preferably, the hydrogen atmosphere is present duringthe heat treatment at a pressure of from about 10 Torr to about 2000Torr, and more preferably from about 100 Torr to about 1000 Torr, andmost preferably from about 100 Torr to about 930 Torr. Mixtures of H₂and an inert gas such as Ar can be used. Also, H₂ in N₂ can be used toeffect control of the N₂ level of the niobium oxide.

During the heat treatment process, a constant heat treatment temperaturecan be used during the entire heat treating process or variations intemperature or temperature steps can be used. For instance, hydrogen canbe initially admitted at 1000° C. followed by increasing the temperatureto 1250° C. for 30 minutes followed by reducing the temperature to 1000°C. and held there until removal of the H₂ gas. After the H₂ or otheratmosphere is removed, the furnace temperature can be dropped.Variations of these steps can be used to suit any preferences of theindustry.

The oxygen reduced niobium oxides can also contain levels of nitrogen,e.g., from about 100 ppm to about 80,000 ppm N₂ or to about 130,000 ppmN₂. Suitable ranges includes from about 31,000 ppm N2 to about 130,000ppm N₂ and from about 50,000 ppm N₂ to about 80,000 N₂.

The oxygen reduced niobium oxide is any niobium oxide which has a loweroxygen content in the metal oxide compared to the starting niobiumoxide. Typical reduced niobium oxides comprise NbO, NbO_(0.7),NbO_(1.1), NbO₂, and any combination thereof with or without otheroxides present. Generally, the reduced niobium oxide of the presentinvention has an atomic ratio of niobium to oxygen of about 1:less than2.5, and preferably 1:2 and more preferably 1:1.1, 1:1, or 1:0.7. Putanother way, the reduced niobium oxide preferably has the formulaNb_(x)O_(y), wherein Nb is niobium, x is 2 or less, and y is less than2.5x. More preferably x is 1 and y is less than 2, such as 1.1, 1.0,0.7, and the like.

The starting niobium oxides can be prepared by calcining at 1000° C.until removal of any volatile components. The oxides can be sized byscreening. Preheat treatment of the niobium oxides can be used to createcontrolled porosity in the oxide particles.

The reduced niobium oxides of the present invention also preferably havea microporous surface and preferably have a sponge-like structure,wherein the primary particles are preferably 1 micron or less. The SEMsfurther depict the type of preferred reduced niobium oxide of thepresent invention. As can be seen in these microphotographs, the reducedniobium oxides of the present invention can have high specific surfacearea, and a porous structure with approximately 50% porosity. Further,the reduced niobium oxides of the present invention can be characterizedas having a preferred specific surface area of from about 0.5 to about10.0 m 2/g, more preferably from about 0.5 to 2.0 m²/g, and even morepreferably from about 1.0 to about 1.5 m 2/g. The preferred apparentdensity of the powder of the niobium oxides is less than about 2.0 g/cc,more preferably, less than 1.5 g/cc and more preferably, from about 0.5to about 1.5 g/cc.

The various oxygen reduced niobium oxides of the present invention canbe further characterized by the electrical properties resulting from theformation of a capacitor anode using the oxygen reduced niobium oxidesof the present invention. In general, the oxygen reduced niobium oxidesof the present invention can be tested for electrical properties bypressing powders of the oxygen reduced niobium oxide into an anode andsintering the pressed powder at appropriate temperatures and thenanodizing the anode to produce an electrolytic capacitor anode which canthen be subsequently tested for electrical properties.

Accordingly, another embodiment of the present invention relates toanodes for capacitors formed from the oxygen reduced niobium oxides ofthe present invention. Anodes can be made from the powdered form of thereduced oxides in a similar process as used for fabricating metalanodes, i.e., pressing porous pellets with embedded lead wires or otherconnectors followed by optional sintering and anodizing. The leadconnector can be embedded or attached at any time before anodizing.Anodes made from some of the oxygen reduced niobium oxides of thepresent invention can have a capacitance of from about 1,000 CV/g orlower to about 300,000 CV/g or more, and other ranges of capacitance canbe from about 20,000 CV/g to about 300,000 CV/g or from about 62,000CV/g to about 200,000 CV/g and preferably from about 60,000 to 150,000CV/g. In forming the capacitor anodes of the present invention, asintering temperature can be used which will permit the formation of acapacitor anode having the desired properties. The sintering temperaturewill be based on the oxygen reduced niobium oxide used. Preferably, thesintering temperature is from about 1200° C. to about 1750° C. and morepreferably from about 1200° C. to about 1400° C. and most preferablyfrom about 1250° C. to about 1350° C. when the oxygen reduced niobiumoxide is an oxygen reduced niobium oxide.

The anodes formed from the niobium oxides of the present invention arepreferably formed at a voltage of about 35 volts and preferably fromabout 6 to about 70 volts. When an oxygen reduced niobium oxide is used,preferably, the forming voltages are from about 6 to about 50 volts, andmore preferably from about 10 to about 40 volts. Other high formationvoltages can be used such as from about 70 volts to about 130 volts. TheDC leakage achieved by the niobium oxides of the present invention haveprovided excellent low leakage at high formation voltages. This lowleakage is significantly better than capacitors formed with Nb powder ascan be seen in, for instance, FIG. 12. Anodes of the reduced niobiumoxides can be prepared by fabricating a pellet of Nb₂O₅ with a lead wirefollowed by sintering in H₂ atmosphere or other suitable atmosphere inthe proximity of a getter material just as with powdered oxides. In thisembodiment, the anode article produced can be produced directly, e.g.,forming the oxygen reduced valve metal oxide and an anode at the sametime. Also, the anodes formed from the oxygen reduced niobium oxides ofthe present invention preferably have a DC leakage of less than about5.0 nA/CV. In an embodiment of the present invention, the anodes formedfrom some of the oxygen reduced niobium oxides of the present inventionhave a DC leakage of from about 5.0 nA/CV to about 0.50 nA/CV.

The present invention also relates to a capacitor in accordance with thepresent invention having a niobium oxide film on the surface of thecapacitor. Preferably, the film is a niobium pentoxide film. The meansof making metal powder into capacitor anodes is known to those skilledin the art and such methods such as those set forth in U.S. Pat. Nos.4,805,074, 5,412,533, 5,211,741, and 5,245,514, and European ApplicationNos. 0 634 762 Al and 0 634 761 A1, all of which are incorporated intheir entirety herein by reference.

The capacitors of the present invention can be used in a variety of enduses such as automotive electronics, cellular phones, computers, such asmonitors, mother boards, and the like, consumer electronics includingTVs and CRTs, printers/copiers, power supplies, modems, computernotebooks, disc drives, and the like.

The present invention will be further clarified by the followingexamples, which are intended to be exemplary of the present invention.

TEST METHODS

-   Anode Fabrication:    -   size—0.197″ dia    -   3.5 Dp    -   powder wt=341 mg    -   Anode Sintering:        -   1300° C. 10′        -   1450° C. 10′        -   1600° C. 10′        -   1750° C. 10′    -   30V Ef Anodization:        -   30V Ef @ 60° C./0.1% H₃PO₄ Electrolyte            -   20 mA/g constant current    -   DC Leakage/Capacitance—FSR Testing:        -   DC Leakage Testing            -   70% Ef (21 VDC) Test Voltage            -   60 second charge time            -   10% H₃PO₄ @ 21° C.        -   Capacitance—DF Testing:            -   18% H₂SO₄ @ 21° C.            -   120 Hz    -   50V Ef Reform Anodization:        -   50V Ef @ 60° C./0.1% H₃PO₄ Electrolyte            -   20 mA/g constant current    -   DC Leakage/Capacitance—ESR Testing:        -   DC leakage Testing            -   70% Ef (35 VDC) Test Voltage            -   60 second charge time            -   10% H₃PO₄ @ 21° C.        -   Capacitance—DF Testing:            -   18% H₂SO₄ @ 21° C.            -   120 Hz-   75V Ef Reform Anodization:    -   75V Ef @ 60° C/0.1% H₃PO₄ Electrolyte        -   20 mA/g constant current    -   DC Leakage/Capacitance—ESR Testing:        -   DC leakage Testing            -   70% Ef (52.5 VDC) Test Voltage            -   60 second charge time            -   10% H₃PO₄ @ 21° C.        -   Capacitance—DF Testing:            -   18% H₂SO₄ @ 21° C.            -   120 Hz                Scott Density, oxygen analysis, phosphorus analysis, and                BET analysis were determined according to the procedures                set forth in U.S. Pat. Nos. 5,011,742; 4,960,471; and                4,964,906, all incorporated hereby in their entireties                by reference herein.

EXAMPLES Example 1

+10 mesh Ta hydride chips (99.2 gms) with approximately 50 ppm oxygenwere mixed with 22 grams of Nb₂O₅ and placed into Ta trays. The trayswere placed into a vacuum heat treatment furnace and heated to 1000° C.H₂ gas was admitted to the furnace to a pressure of +3 psi. Thetemperature was further ramped to 1240° C. and held for 30 minutes. Thetemperature was lowered to 1050° C. for 6 minutes until all H₂ was sweptfrom the furnace. While still holding 1050° C., the argon gas wasevacuated from the furnace until a pressure of 5×10⁻⁴ torr was achieved.At this point 700 mm of argon was readmitted to the chamber and thefurnace cooled to 60° C.

The material was passivated with several cyclic exposures toprogressively higher partial pressures of oxygen prior to removal fromthe furnace as follows: The furnace was backfilled with argon to 700 mmfollowed by filling to one atmosphere with air. After 4 minutes thechamber was evacuated to 10⁻² torr. The chamber was then backfilled to600 mm with argon followed by air to one atmosphere and held for 4minutes. The chamber was evacuated to 10⁻² torr. The chamber was thenbackfilled to 400 mm argon followed by air to one atmosphere. After 4minutes the chamber was evacuated to 10⁻² torr. The chamber was thembackfilled to 200 mm argon followed by air to one atmosphere and heldfor 4 minutes. The chamber was evacuated to 10⁻² torr. The chamber wasbackfilled to one atmosphere with air and held for 4 minutes. Thechamber was evacuated to 10⁻² torr. The chamber was backfilled to oneatmosphere with argon and opened to remove the sample.

The powder product was separated from the tantalum chip getter byscreening through a 40 mesh screen. The product was tested with thefollowing results. CV/g of pellets sintered to 1300° C. × 81,297 10minutes and formed to 35 volts = nA/CV (DC leakage) = 5.0 SinteredDensity of pellets = 2.7 g/cc Scott density = 0.9 g/cc Chemical Analysis(ppm) C = 70 H₂ = 56 Ti = 25 Mn = 10 Sn = 5 Cr = 10 Mo = 25 Cu = 50 Pb =2 Fe = 25 Si = 25 Ni = 5 Al = 5 Mg = 5 B = 2 all others <limits

Example 2

Samples 1 through 20 are examples following similar steps as above withpowdered Nb₂O₅ as indicated in the Table. For most of the examples, meshsizes of the starting input material are set forth in the Table, forexample 60/100, means smaller than 60 mesh, but larger than 100 mesh.Similarly, the screen size of some of the Ta getter is given as 14/40.The getters marked as “Ta hydride chip” are +40 mesh with no upper limiton particle size.

Sample 18 used Nb as the getter material (commercially available N200flaked Nb powder from CPM). The getter material for sample 18 was finegrained Nb powder which was not separated from the final product. X-raydiffraction showed that some of the getter material remained as Nb, butmost was converted to NbO_(1.1) and NbO by the process as was thestarting niobium oxide material Nb₂O₅.

Sample 15 was a pellet of Nb₂O₅, pressed to near solid density, andreacted with H₂ in close proximity to the Ta getter material. Theprocess converted the solid oxide pellet into a porous slug of NbOsuboxide. This slug was sintered to a sheet of Nb metal to create ananode lead connection and anodized to 35 volts using similar electricalforming procedures as used for the powder slug pellets. This sampledemonstrates the unique ability of this process to make a ready toanodize slug in a single step from Nb₂O₅ starting material.

The Table shows the high capacitance and low DC leakage capable ofanodes made from the pressed and sintered powders/pellets of the presentinvention. Microphotographs (SEMs) of various samples were taken. Thesephotographs show the porous structure of the reduced oxygen niobiumoxide of the present invention. In particular, FIG. 1 is a photograph ofthe outer surface of a pellet taken at 5,000×(sample 15). FIG. 2 is aphotograph of the pellet interior of the same pellet taken at 5,000×.FIGS. 3 and 4 are photographs of the outer surface of the same pellet at1,000×. FIG. 5 is a photograph of sample 11 at 2,000× and FIGS. 6 and 7are photographs taken of sample 4 at 5,000×. FIG. 8 is a photographtaken of sample 3 at 2,000× and FIG. 9 is a photograph of sample 6 at2,000×. Finally, FIG. 10 is a photograph of sample 6, taken at 3,000×and FIG. 11 is a photograph of sample 9 taken at 2,000×. XRD* XRD* XRD*XRD* 1300 × 1300 × Temp Time Hydrogen Major Major Minor Minor 35v 35vSample Input Material Gms Input Getter Gms (° C.) (min) Pressure 1** 2**1*** 2*** CV/g na/CV 1 −40 mesh 20 (est) Ta hydride chips 40 (est) 124030  3 psi 81297 5 calcined Nb₂O₅ 2  60/100 Nb₂0₅ 23.4 Ta hydride chips65.4 1250 30  3 psi NbO_(1.1) NbO TaO 115379 1.28 3  60/100 Nb₂O₅ 23.4Ta hydride chips 65.4 1250 30  3 psi NbO_(1.1) NbO TaO 121293 2.19 4100/325 Nb₂O₅ 32.3 Ta hydride chips 92.8 1250 30  3 psi 113067 1.02 5100/325 Nb₂O₅ 32.3 Ta hydride chips 92.8 1250 30  3 psi 145589 1.42 6 60/100 Nb₂O₅ 26.124 Ta hydride chips 72.349 1250 90  3 psi 17793 12.867  60/100 Nb₂O₅ 26.124 Ta hydride chips 72.349 1250 90  3 psi 41525 5.638 200/325 Nb₂O₅ 29.496 Ta hydride chips 83.415 1250 90  3 psi 1779016.77 9  60/100 Nb₂O₅ 20.888 Ta hydride chips 60.767 1200 90  3 psiNbO_(1.1) NbO Ta₂O₅ 63257 5.17 10  60/100 Nb₂O₅ 20.888 Ta hydride chips60.767 1200 90  3 psi NbO_(1.1) NbO Ta₂O₅ 69881 5.5 11 200/325 Nb₂O₅23.936 Ta hydride chips 69.266 1200 90  3 psi NbO_(1.1) NbO Ta₂O₅ 617166.65 12 200/325 Nb₂O₅ 23.936 Ta hydride chips 69.266 1200 90  3 psiNbO_(1.1) NbO Ta₂O₅ 68245 6.84 13 200/325 Nb₂O₅ 15.5 14/40 Ta hydride41.56 1250 30  3 psi NbO_(0.7) NbO TaO NbO₂ 76294 4.03 14 200/325 Nb2O510.25 14/40 Ta hydride 68.96 1250 30  3 psi NbO_(0.7) NbO TaO NbO₂ 2928121.03 15 Nb₂O₅ pellets 3.49 14/40 Ta hydride 25.7 1250 30  3 psi 708400.97 16 200/325 Nb₂O₅ 13.2 14/40 Ta hydride 85.7 1200 30  3 psi NbO₂NbO_(0.7) TaO NbO 5520 34.33 17 200/325 Nb₂O₅ 14.94 14/40 Ta hydride41.37 1200 30  3 psi 6719 38.44 18 200/325 Nb₂O₅ 11.92 N200 Nb powder21.07 1200 30  3 psi Nb NbO_(1.1) NbO 25716 4.71 19 200/325 Nb₂O₅ 1014/40 Ta hydride 69 1250 30 100 Torr 108478 1.95 20 200/325 Nb₂O₅ 1614/40 Ta hydride 41 1250 30 100 Torr 106046 1.66*X-Ray Defraction Analysis Results**Major 1 and 2 refer to primary components present by weight.***Minor 1 and 2 refer to secondary components present by weight.Samples 11 and 12 had the same input material. Samples 2 and 3 had thesame input material.Samples 6 and 7 had the same input material. Samples 9 and 10 had thesame input material.

Example 3

This experiment was conducted to show the ability of the niobium oxidesof the present invention to form at high formation voltages and yetretain an acceptable DC leakage. The niobium oxide of the presentinvention was compared to a capacitor formed from commercially availabletantalum and niobium metal. In particular, Table 2 sets forth the basiccharacteristics of the materials that were used to form the capacitorfor this example. The C606 tantalum is a commercially available productfrom Cabot Corporation. The niobium oxide used in Example 3 was preparedin manner similar to Example 1. Table 3 further set forth the chemicalcompositions of components other than the niobium metal for the niobiumoxide of the present invention and the niobium metal which was used forcomparison purposes. Tables 4-7 set forth the data obtained for eachformation voltage starting at 15 volts and ending at 75 volts. The datais also plotted in FIG. 12. The particular capacitor anodes which weretested for DC leakage were formed using the stated formation voltage andin each case the sintering temperature was 1300° C. for 10 minutes andthe formation temperature of the anode was 60° C. with the press densityset forth in Table 2. Further, the anodes were formed in 0.1% H₃PO₄electrolyte, with a 135 milliamps/g constant current up to the desiredformation voltage which was held for 3 hours. The test conditions werethe same as for the DC leakage tested in Example 1 (except as notedherein) including 10% H₃PO₄ at 21° C. The anode size of the Nb suboxidewas 0.17 inch diameter. The anode size of the tantalum was 0.13 inchdiameter and the anode size for the niobium was 0.19 inch diameter. Theanode weight was as follows: niobium suboxide=200 mg; tantalum=200 mg;niobium=340 mg. TABLE 2 Nb Ta C606 Sub-Oxide Nb (Commercial product)BET, m²/g 0.75 0.58 Commercial spec Scott density, g/in² 20.7 23.8Commercial spec Anode sintering 3.0 4.1 5.3 density, g/cc CV/g 56,56222,898 61,002 Sintering conditions 10 min 10 min 10 min @ 1300° C. @1300° C. @ 1300° C. Formation 60° C. 60° C. 60° C. temperature

TABLE 3 Element Nb Oxide Nb C 150 422 O 141,400 2399 H 55 Si 30 250 Ni10 20 Fe 200 100 Cr 40 50 Ti <5 <5 Mn 25 25 Sn <5 <5 Ca <50 <50 Al 50 20W <100 <100 Zr <5 <5 Mg 25 10 B <5 10 Co <5 <5 Cu <5 10

As can be seen in FIG. 12 and Tables 4-7, while the DC leakage forcapacitor anodes made from niobium metal increased dramatically at aformation voltage of 75 volts, the DC leakage for the capacitor anodeformed from a niobium oxide of the present invention remain relativelystable. This is quite impressive considering the effect seen withrespect to a capacitor anode formed from niobium metal. Thus, unlikeniobium metal, the niobium oxides of the present invention have theability to be formed into capacitor anodes and formed at high voltageswhile maintaining acceptable DC leakage which was not possible withanodes made simply from niobium metal. Thus, the niobium oxides of thepresent invention can be possible substitutes for anodes made fromtantalum in certain applications which is quite beneficial consideringniobium can be less expensive. TABLE 4 Nb Sub-Oxide Ta Ta Nb Anodization15.0 15.0 15.0 15.0 Voltage (CV) 11,037 13,095 12,635 7,893 (CV/g)56,562 63,154 61,002 22,898 (CV/g) (Corr) (CV/cc) 168,304 352,254324,448 93,372 (Ohms) 0.82 0.92 0.90 0.89 Charge time 30 30 30 30 one(sec) (uA) 72.86 10.94 12.74 13.14 *“FLIERS” 0 0 0 0 “GASSERS” 0 0 0 0 N= 8 8 8 2 (uA/g) 373.37 52.75 61.51 38.12 (nA/CV) 6.60 0.84 1.01 1.66Charge time 60 60 60 60 two (sec) (uA) 60.08 7.39 9.00 9.42 “FLIERS” 0 00 0 “GASSERS” 0 0 0 0 N = 8 8 8 2 (uA/g) 307.90 35.63 43.45 27.31(nA/CV) 5.44 0.56 0.71 1.19 Dia. Shkg(%) 0.6 0.6 −1.2 4.0 Ds(g/cc) 3.05.6 5.3 4.1

TABLE 5 Nb Sub-Oxide Ta Ta Nb Anodization 35.0 35.0 35.0 35.0 Voltage(CV) 10,445 12,678 12,130 7,977 (CV/g) 53,107 60,470 58,448 23,457(CV/g) (Corr) (CV/cc) 158,416 341,045 311,482 93,700 (Ohms) 0.92 1.041.02 0.95 Charge time 30 30 30 30 one (sec) (uA) 54.13 11.50 29.60 53.31*“FLIERS” 0 1 0 0 “GASSERS” 0 0 0 0 N = 8 8 8 2 (uA/g) 275.23 54.86142.64 156.77 (nA/CV) 5.18 0.91 2.44 6.68 Charge time 60 60 60 60 two(sec) (uA) 47.21 7.56 20.99 31.17 “FLIERS” 0 1 0 0 “GASSERS” 0 0 0 0 N =8 8 8 2 (uA/g) 240.04 36.08 101.14 91.66 (nA/CV) 4.52 0.60 1.73 3.91Dia. Shkg(%) 0.6 0.6 −1.2 3.8 Ds(g/cc) 3.0 5.6 5.3 4.0

TABLE 6 Nb Sub-Oxide Ta Ta Nb Anodization 55.0 55.0 55.0 55.0 Voltage(CV) 9,476 11,448 10,878 7,894 (CV/g) 47,159 54,928 52,394 22,941 (CV/g)(Corr) (CV/cc) 134,774 307,960 279,339 92,880 (Ohms) 1.35 1.21 1.18 1.08Charge time 30 30 30 30 one (sec) (uA) 53.70 13.48 28.40 61.61 *“FILERS”0 0 0 0 “GASSERS” 0 0 0 0 N = 8 8 8 2 (uA/g) 267.23 64.65 136.80 179.05(nA/CV) 5.67 1.18 2.61 7.80 Charge time 60 60 60 60 two (sec) (uA) 46.288.91 20.24 36.29 “FLIERS” 0 0 0 0 “GASSERS” 0 0 0 0 N = 8 8 8 2 (uA/g)230.34 42.77 97.50 105.45 (nA/CV) 4.88 0.78 1.86 4.60 Dia. Shkg(%) 0.30.6 −1.2 3.8 Ds(g/cc) 2.9 5.6 5.3 4.0

TABLE 7 Nb Sub-Oxide Ta Ta Nb Anodization 75.0 75.0 75.0 75.0 Voltage(CV) 5,420 10,133 9,517 7,872 (CV/g) 27,508 48,484 45,749 22,886 (CV/g)(Corr) (CV/cc) 80,768 274,194 246,127 93,954 (Ohms) 4.58 1.37 1.31 1.31Charge time 30 30 30 30 one (sec) (uA) 67.08 16.76 27.47 640.50*“FLIERS” 0 0 0 0 “GASSERS” 0 0 0 0 N = 8 8 8 2 (uA/g) 340.40 80.17132.04 1862.19 (nA/CV) 12.37 1.65 2.89 81.37 Charge time 60 60 60 60 two(sec) (uA) 55.91 10.97 19.90 412.20 “FLIERS” 0 0 0 0 “GASSERS” 0 0 0 0 N= 8 8 8 2 (uA/g) 283.75 52.48 95.67 1198.43 (nA/CV) 10.32 1.08 20.952.37 Dia. Shkg(%) 0.1 0.9 −0.9 4.3 Ds(g/cc) 2.9 5.7 5.4 4.14

Other embodiments of the present invention will be apparent to thoseskilled in the art from consideration of the specification and practiceof the invention disclosed herein. It is intended that the specificationand examples be considered as exemplary only, with a true scope andspirit of the invention being indicated by the following claims.

1. A capacitor anode comprising a niobium oxide having an atomic ratioof niobium to oxygen of 1:less than 2.5 and being formed at a formationvoltage of about 6 volts or higher.
 2. The capacitor anode of claim 1,wherein said capacitor anode is formed at a formation voltage of fromabout 6 to about 130 volts.
 3. The capacitor anode of claim 1, whereinsaid capacitor anode is formed at a formation voltage of from about 75volts to about 130 volts.
 4. The capacitor anode of claim 1, whereinsaid capacitor anode is formed at a formation voltage of from about 75volts to about 100 volts.
 5. The capacitor anode of claim 1, whereinsaid DC leakage is less than 15 nA/CV, wherein said DC leakage isdetermined at a sintering temperature of 1300° C. for 10 minutes and aformation temperature of 60° C.
 6. The capacitor anode of claim 5,wherein said DC leakage is less than about 12 nA/CV.
 7. The capacitoranode of claim 3, wherein said DC leakage is less than 15 nA/CV.
 8. Aniobium oxide having an atomic ratio of niobium to oxygen of 1 less than2.5, and having a nitrogen content of from about 31,000 ppm N₂ to about130,000 ppm N₂. 9-31. (canceled)